In tape drive systems that utilize a single tape cartridge reel, once the cartridge is loaded and is registered at the appropriate datum, the tooth ring coupling of the cartridge reel becomes engaged with the motor system of the tape drive. The lead end of the tape, which is called the leader block or leader pin, is then transferred from the cartridge reel to the take up reel located inside the tape drive. This take up reel is also attached to a motor system. Once a leader pin has been successfully moved to the take up reel, the tape is located against the magnetic head of the tape drive and both of the reels of the tape drive are ready to be rotated by the motor/encoder, to start the read/write process.
The motor/encoder system of a tape drive may have a number of functions, depending on the design of the tape drive. For example, the motor/encoder system can control the tape speed, regulate tape tension and align the take-up reel at a precise location to properly receive the leader pin.
As the form-factor requirement of single reel cartridge tape drives decreases, the size of the components used to create the tape drive also diminish. Recent tape drives the use LTO cartridges have a form factor requirement of 5¼ inch. One of the requirements of this form factor is that the entire tape drive must fit into a height of 3¼ inch. Therefore, the motor/encoder system must also be designed to fit and properly function in a very limited space.
Motor/encoder systems for precisely controlling the motor speed are known. In many such systems, the motor and the encoder are separate, individual components. The problem with this type of design is the space required to accommodate two separate parts; the motor and the encoder. In a tape drive system with a form-factor requirement, there is no space available for two separate motor and encoder components. Furthermore, providing two separate components normally have a higher cost in comparison to provision of a single component having dual functionality. It also adds assembly time and added cost of inventory.
Another concern of certain encoding arrangements arises because of the use of a magnetic shaft encoder that employs a gear or a toothed wheel for inducing periodic electrical pulses in an inductive pick-up. The teeth of the wheel are evenly spaced and every tooth generates a signal as it passes the pick-up. One problem with such an encoder is its relatively limited resolution. This is because the size of the tooth is limited in how small the tooth can be made. In other arrangements, a magnetic code wheel is employed. Such arrangements use an inductive coil concept or a moving coil, movable together with a rotor, that interacts with the magnetic code wheel. A major concern with such an application is routing of the wire from the movable coil mounted at the center of the rotor. It requires a rotary shaft having a through hole formed along the axis of rotation of the motor's shaft to route the coil lead wires.
There is a need for an arrangement in which the motor/encoder system is packaged in the smallest practical volume, yet provide the functions of housing a DC brushless motor with its driver circuitry, a magnetic encoder with necessary sensors and provide precision mounting and locating features for a cartridge driver component.